In the voice we can recognize the properties noted in other kinds of sound. These are quality, pitch and intensity.

1. The quality of vocal sound is almost endless in variety, as is shown by the vocal capabilities of different individuals. The quality of any musical sound depends upon the relative power of the fundamental tone, and of the overtones that accompany it. The less the fundamental tone is disturbed by overtones, the clearer and better is the voice. This difference in quality of the human voice depends upon the perfectness of the elasticity, the relation of thickness to length, surface smoothness, and other physical conditions of the cords themselves, and the exactitude with which the muscles can adapt the surfaces. For "singing well, much more is necessary than good quality of tone, which is common enough. The muscles of the larynx, thorax, and mouth must all be educated to an extraordinarily high degree.

2. The pitch of the notes produced in the larynx depends upon - first, the absolute length of the vocal cords. This varies with age, particularly in males, whose vocal organs undergo rapid growth at puberty, when vocalization is uncertain from the rapid changes going on in the part; hence the voice is said to crack. The vocal cords of women have been found by measurement to be about one-third shorter than those of men, and people with tenor voices have shorter cords than basses or baritones. Secondly, on the tension of the cords: the tighter the vocal cords are drawn by the crico-thyroid muscles, the higher the notes produced; and the well-known singer Garcia believed he observed with the laryngoscope the vocal processes so tightly pressed together as to impede the vibration of the posterior part of the cords, and by this means they could be voluntarily shortened.

3. Intensity or loudness of the voice depends on the strength of the current of air. The more powerful the air blast the greater the amplitude of the vibrations, and hence the greater the sound produced. The narrower the chink of the glottis, and the tighter the parallel cords are stretched, the less is the amount of air and the weaker is the blast required to set them vibrating; and vice versa, the looser the cords and the wider apart they are, the greater the volume and the force of the air current necessary for their complete vibration. Hence it is that an intense vibration or loud note can be produced much more easily with notes of a high pitch than with very low notes, and we find singers choosing for their telling crescendo some note high up in the range of their voice.

The human voice, including every kind, extends over about three and a half octaves. -Of this wide range a single individual can seldom sing more than two octaves. The soprano, alto, tenor, and bass forming a descending series, the range of each one of which considerably overlaps the next in the scale.

During the ordinary vocal sounds, the air, both in the resonating tubes above the larynx and in the windpipe coming from below, is set vibrating, so that the trachea and bronchi act as resonators as well as the pharynx, mouth, etc. This may be recognized by placing the hand on the thorax, when a distinct vibration is communicated from the chest wall. Such tones are, therefore, spoken of as chest notes. Besides the chest tones of the ordinary voice, we can produce notes of a higher pitch and a different quality, which are called head notes, since their production is not accompanied by any vibration of the chest wall. The physical contrivance by means of which this falsetto voice is brought about is not very clearly made out. The following are the more probable views: (i) It has been suggested that in falsetto only the thin edges of the cord vibrate, the internal thyro-arytenoid muscles keeping the base of the cord fixed; while with chest tones a greater surface of the cord is brought into play. (2) The cords are said to be wider apart in falsetto than in chest notes, and hence the trachea, etc., ceases to act as a resonator. (3) Or the cords may be arranged so that only one part of them, the anterior, can vibrate, and thus they act as shortened cords, a "stop" being placed on the point where the vibrations cease, by the internal thyro-arytenoid muscle.

The production of a falsetto voice is distinctly voluntary, and is probably dependent upon some muscular action in immediate relation to the cords, for it is always associated with a sensation of muscular exertion in the larynx, as well as with changes that take place in the conformation of the mouth and other resonating tubes.